Vanadium Oxide Nanotubes

Synthesis Vanadium oxide nanotubes (VO_x-NTs) are easily accessible as a pure product in gram quantities by a low-temperature, soft chemistry synthesis. Primary alkyl amines (C_nH_2n+1NH₂ with n = 4 - 22) or alkyl diamines (H₂N[CH₂]_nNH₂ with n = 14 - 20) are reacted with a vanadium(V) alkoxide, and, after aging and a hydrothermal treatment at 180 C for about 1 week, the nanotubes are obtained in very high yield.
Morphology The tubular structure can be already seen in high-resolution SEM images. The inner core appears to be empty while the tube walls show roll-up characteristics.
Structural Characterization
	TEM investigations reveal that the tubes have an empty core and that a layered structure builds up the tube walls.

TEM image of cross-sections (left): a tube consisting of concentric shells (upper left part) and a single-layer scroll (upper right part) are present. Vanadium map obtained by ESI (middle): sites containing V (bright contrast) appear at the same sites as the dark contrast in the TEM image. Carbon map (right): C is present around the tubes and in their core due to the organic embedding material used for the cross-sectional preparation. A simple structural model for the tube walls could be derived from these results: vanadium oxide layers between which the amine molecules are embedded form the walls. Information obtained in reciprocal space by X-ray and electron diffraction led to a decription of the nanotube structure by a cell with a tetragonal metric (a = 0.62 nm and c being equal to the inter-layer distance). However, one should consider that three-dimensional periodicity is not present in nanotubes due to the bending of the layers. Thus, their structure can only approximately be described in the usual crystallographic terms.

	A structural model for the wall structure of the VO_x-NTs was derived in relation to a new crystalline vanadate. The X-ray powder diffractogram calculated with this models matches well with the simulated one.
Selected Publications Redox-Active Nanotubes of Vanadium Oxide M.E. Spahr, P. Bitterli, R. Nesper, M. Müller, F. Krumeich, and H.-U. Nissen, Angew. Chem. Int. Ed. 37 (1998) 1263-1265 DOI Morphology and Topochemical Reactions of Novel Vanadium Oxide Nanotubes F. Krumeich, H.-J. Muhr, M. Niederberger, F. Bieri, B. Schnyder, and R. Nesper, J. Am. Chem Soc. 121 (1999) 8324-8331 DOI Vanadium Oxide Nanotubes - a New Flexible Vanadate Nanophase H.-J. Muhr, F. Krumeich, U.P. Schönholzer, F. Bieri, M. Niederberger, L.J. Gauckler, and R. Nesper, Adv. Mater. 12 (2000) 231-234 DOI Low-Cost Synthesis of Vanadium Oxide Nanotubes via Two Novel Non-Alkoxide Routes M. Niederberger, H.-J. Muhr, F. Krumeich, F. Bieri, D. Günther, and R. Nesper, Chem. Mater. 12 (2000) 1995-2000 DOI Controlled Uptake and Release of Metal Cations by Vanadium Oxide Nanotubes J.M. Reinoso, H.-J. Muhr, F. Krumeich, F. Bieri, and R. Nesper, Helv. Chim. Acta 83 (2000) 1724-1733 DOI The Cross-Sectional Structure of Vanadium Oxide Nanotubes Studied by Transmission Electron Microscopy and Electron Spectroscopic Imaging F. Krumeich, H.-J. Muhr, M. Niederberger, F. Bieri, and R. Nesper, Z. anorg. allg. Chem. 626 (2000) 2208-2216 DOI The First Oxide Nanotubes with Alternating Inter-Layer Distances Krishnan S. Pillai, F. Krumeich, H.-J. Muhr, M. Niederberger, and R. Nesper, Solid State Ionics 411-412 (2001) 185-190 DOI Flexible V₇O₁₆ Layers as the Common Structural Element of Vanadium Oxide Nanotubes and a New Crystalline Vanadate M. Wörle, F. Krumeich, F. Bieri, H.-J. Muhr, and R. Nesper, Z. anorg. allg. Chem. 628 (2002) 2778-2784 DOI

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